Control of water treatment system with low level boron detection

ABSTRACT

A water treatment system and method including a membrane-based boron removal unit includes a boron analyzer for detecting the concentration of boron in a treatment stream. The boron removal unit can be a reverse osmosis (RO) or electrodeionization (EDI) treatment unit. A controller responds to the detected boron concentration to control an operation of the RO or EDI units. In an EDI system, the controller may adjust current or voltage supplied to match current to changes in ionic load and maintain a portion of the dilute cell in a substantially regenerated state. In an RO system, the controller may control the high pressure side flow rate, the brine blowdown rate, the product water permeation rate, pH, or feed rate of chemicals in response to the detected boron concentration value.

This application claims the benefit of U.S. provisional applicationsNos. 60/327,666, filed Oct. 5, 2001 and 60/348,400, filed Oct. 26, 2001.

FIELD OF THE INVENTION

The present invention relates generally to methods and apparatus forcontrolling and/or regulating operation of water treatment systems toenhance or optimize treatment, wherein the treatment system removesboron. It relates more particularly to water treatment or ultrapurewater (UPW) treatment systems employing an arrangement of various watertreatment units that include one or more reverse osmosis (RO) treatmentunits, or to systems that include one or more filled cellelectrodialysis (EDI) units. In broad terms, such control is effected bysampling the liquid being treated, providing a sample or a sample streamto a boron analyzer, and applying the detected boron level to set anoperating parameter or processing condition of an RO or EDI unit so asto enhance the treatment or removal process. Sampling may be performedeither before, within or after such EDI or RO unit, and in someembodiments is performed at a product outlet, such as a primary make-upline outlet in a semiconductor plant, using a low-level on-line borondetector.

BACKGROUND OF THE INVENTION

It has become increasingly important to be able to detect, measure andremove very low concentrations of contaminants in deionized water with ahigh degree effectiveness and reproducibility of results. For municipalwater supplies, certain maximum contaminant levels (e.g., 500 ppb forboron) must not be exceeded, while for certain industrial applications,such as semiconductor manufacture, levels below about 100 ppt aredesirable. This is because even very low levels of boron present in thedeionized UPW product water used in manufacturing can significantly andadversely affect the quality and performance of a semiconductor chip.

Large amounts of ultrapure water are required in processes tomanufacture semiconductors, and boron may be present as a contaminant inthe raw or pretreated feed water. If present, it must be removed to verylow concentration, for the following reason. Boron is a p-typesemiconductor dopant used in manufacture of solid state electronics, andit functions as a principal charge carrier in the doped silicon crystal.The presence of boron even at a sub ppb level in a fab plant processfluid, such as developer, cleaning fluid, vapor, rinse water or the likecan give rise to surface deposits of boron, which in turn, may becomeincorporated in a silicon substrate during various processstages—particularly heating or ion implantation stages, and may changethe intended dopant profile or otherwise alter the electricalcharacteristics of the substrate. To prevent the inadvertentintroduction of boron contamination during manufacturing processes, itis necessary to remove boron from the fab plant UPW stream down to avery low residual level, typically to a low threshold under 50 ppt, andpreferably below 10-20 ppt.

Several general facts about the sources of and levels of boron presentin natural waters, and its passage in treated waters, affect the abilityof a treatment plant to dependably or economically achieve a productlevel below a set level. Boron may be present in local water sources atlevels of about 50 ppb to several ppm (or more for sea water), so it issometimes necessary when treating bulk water to carry out specific stepsto remove boron to a desired level. One level, in order to meet drinkingwater specifications, may be between 50-500 ppb; this may require a 10-to 100-fold reduction for a seawater reverse osmosis plant. Anotherlevel, suitable for certain agricultural applications (where particularcrops may require a ceiling) is several hundred ppb, and this target maybe set for a plant treating municipal waste, agricultural run-off orbrackish groundwater, among other sources.

Several water treatment technologies achieve some reduction of boron,and may be applied to meet such standards. These include reverseosmosis, various complexing agents followed by filtration, as well asboron selective resins and other treatment approaches. Water treatmentplants typically involve a pretreatment stage followed by a sequence ofother processes, possibly with return loops and bleed or blowdown exitpoints, bypasses and/or blending to meet diverse competing goals ofwater recovery, economy, and safe waste disposal.

A UPW treatment plant for semiconductor fabrication processes mustgenerally demineralize the feed water down to a residual boronconcentration in the product in the low parts per trillion, the preciselevel often being specified for expedience by the boron detection limitof the instrumentation available at the plant. Such a level shall forsimplicity be referred to herein simply as “boron free”.

Boron is generally present in water in a form that is poorly ionized atmiddle pH, and when relying on a reverse osmosis (RO) treatment, about50-70% of the starting boron level may be expected to pass in thepermeate. Much greater removal is possible by raising the pHsubstantially, e.g., to about pH 11, and cuts of 98-99% may be achievedwith RO when the ionic load and membrane characteristics permit an ROunit to be operated in this condition.

Ion exchange is of limited effect. Because boron is poorly captured andis loosely held, it may be said that ion exchange doesn't really stopboron passage, it just slows it down. Generally, boron is poorly ionizedat neutral pH, and is poorly captured and is weakly held by ion exchangeresins. While it may be effectively captured by fully regenerated resin,it may be eluted by other elements (including OH from the equilibriumdissociation of water) as ionic load in the exchange bed increases.Boron ions are therefore the first ions to leak from the mixed ionexchange resin beds that follow RO or that in some areas constitute aprincipal pretreatment. Leakage can occur as the resin becomesexhausted, and will also occur (in the case of boron) in pulses orspikes much earlier, as bleeding due to displacement by an influx ofcompeting ions, or due to a change in temperature, pH or the like.

System design must therefore address the dependable and effectiveremoval of boron to a predetermined level despite the relatively widerange of possible starting concentrations and competing minerals, theseasonal or episodic changes in source quality and composition, and therelatively variable rates of boron removal or retention using standardwater treatment processes.

An illustration is instructive. S. Malhotra et al. have reported in“Correlation of Boron Breakthrough versus Resistivity and DissolvedSilica in RO/DI System” (Ultrapure Water, May/June 1996. 13(4): p.22-26) that boron was the first ion to break through the ion exchangeresin beds of a water treatment system when they switched to usingthin-film-composite (TFC) membranes in their reverse osmosis (RO) units.The introduction of TFC reverse osmosis (RO) membranes (to replacecellulose acetate RO membranes) was very effective in reducing thesilica passage through the RO apparatus, but the reduction in boronpassage was not as great. This led to quicker boron saturation of theion exchange beds and the observation of unexpected boron breakthroughin a mixed ion exchange resin bed. More generally, once boron hasaccumulated in an ion exchange bed, changes or upsets in operatingconditions may lead to boron release at unacceptable levels. Forexample, an increase in temperature may result in release of thecaptured boron (apparently displaced by the higher levels of thermallydissociated hydroxyl ions); similarly, an increase in the level of oneor more other dissolved components in the feed water may displace someof the captured boron, potentially eluting higher concentrations ofboron than were present in the feed. Thus, standard ion exchange resinsare ill-adapted to producing boron-free water.

Adsorption of borate ion on anion exchange resin or selective boroncapture resin is the most common method to for producing boron freewater. Several systems incorporating this approach have been describedin the patent literature, such as those described in U.S. Pat. Nos.5,811,012 and 5,833,846 of M. Tanabe et al. Those patents showboron-specific ion exchange resin downstream of a degasifier andupstream of a final mixed resin bed, and the patentee reports boronmeasurements by ICP-MS of below 10 ppt (apparently its limit ofdetection). One well-known boron-specific exchange resin that may beused in such applications is Amberlite IRA-743T, manufactured by Rohmand Haas Company. Capture resins are widely used at various stages inother treatment systems to meet a required level.

However, boron-specific removal resins generally shed organic carbon,and for semiconductor applications they must therefore be situatedupstream of other removal processes. To minimize expense, such treatmentmay be implemented on a smaller scale in a treatment branch process tosupply water only for the specific fab processes where boron affectsproduct quality. However, these resins, like other exchange resins,necessarily require the use of hazardous chemicals to regenerate theresins, so their use raises certain environmental or safety (as well asrelated cost) concerns. Moreover, capture resins cost several times asmuch as other exchange resins (e.g., about $500-700 dollars per cubicfoot).

When the product water must meet a predetermined maximum contaminantlevel (MCL) or threshold, particularly when the threshold is very low orthe feed is variable, system design may be difficult or present onlycostly solutions. It is possible that boron removal at higher levels maybe enhanced by certain operating protocols with an RO treatment unitthat would allow a downstream process, such as a polishing loop withvirgin ion exchange resin or a primary makeup loop with ion exchangebottles or capture resin, to effectively remove residual boron (andother material) to sub ppb levels with a reasonable resin lifetimebetween replacements or regeneration. However, identifying treatmentconditions or configurations of treatment units that will have such highlevels of removal and operate stably to produce product water below apredetermined threshold, or to produce UPW fab water with boron at a lowppt level, remains a problem. Use of such systems when chip productionvalued at tens of thousands of dollars per hour are at risk may appearto require substantial verification of the process, or fail safeoperating protocols before gaining acceptance in the industry. Forsystems meeting a higher, less stringent, threshold, the above-describedproperties still make dependable modeling difficult.

Thus, there remains a need for systems and methods that operate tocontinuously and effectively produce UPW product water having a boronlevel below a predetermined level.

There is also a need for water treatment methods and systems to produceUPW water for semiconductor manufacture and other applications, whichremove boron down to very low levels without the use of hazardouschemicals.

In addition there is a need for systems and methods to detect change orupset in a UPW treatment unit, and which control a treatment unit or itsoperating environment to maintain quality of the feed water.

Accordingly, a principal object of this invention is to provide methodsand apparatus for water treatment, wherein the treatment system has aboron output below a predetermined maximum level and employs at leastone RO treatment unit and/or filled cell ED/EDI unit.

It is a general object of this invention to provide methods andapparatus for water treatment in semiconductor manufacturing or otherapplication which require accurate, reliable removal of boron to a lowconcentration, e.g., below a predetermined threshold that is between 0and 500 ppb boron, wherein the system effects a boron detection ormeasurement, and applies such measurement to control or regulate acondition of operation of a filled cell electrodialysis stack, an ROunit or a related flow treatment or flow conditioning unit.

It is also an object of this invention to control a treatment system inaccordance with a boron detection and measurement device, applying aboron level measurement to regulate the electrical current or voltagesupplied to a filled cell electrodialysis stack and/or system.

As applied to an RO system, an object of this invention is to providemethods and apparatus for controlling an operating condition of an ROunit in accordance with a system by sampling water with a borondetection/measurement device and applying the measurement to regulatethe operating condition of an RO unit.

Other objects and advantages of the present invention will in part beobvious and will in part appear hereinafter. The invention accordinglycomprises, but is not limited to, the methods and related apparatus,involving the several steps and the various components, and the relationand order of one or more such steps and components with respect to eachof the others, as exemplified by the following description and theaccompanying drawings.

SUMMARY OF THE INVENTION

The invention is generally directed to methods and apparatus for watertreatment producing boron free water or water that meets a predeterminedboron removal threshold. Systems of the invention include a fluidtreatment line including one or more reverse osmosis or filled cellelectrodialysis (electrodeionization or EDI) units, and employ a boronanalyzer for detecting concentration of boron at a point in thetreatment line. The detected level is applied to set a condition ofoperation. In the case of treatment systems with an ED/EDI unit, thismay be accomplished by setting electrical current or voltage supplied toone or more EDI units (stacks), or changing a condition such as pH offluid entering that portion of the system, as a function of the detectedboron level. A control system responsive to the detection level maycontrol the stack to increase its boron removal rate by raising theapplied current or voltage when the boron concentration is greater thana desired value, or may decrease the current or voltage when the boronconcentration is less than a desired value. In this way such stacks orsystems can be operated to treat liquids to a predetermined boronconcentration without the attention of a human operator and withoutwasting excessive electrical current or voltage supplied to such stacksor systems. The control system may alternatively apply the detectedboron level to identify functionally related changes in resin state orfeedwater ionic load, and may change operating parameters to assuresteady state output water quality or to correct an upset condition ordeleterious operating condition. Other control steps initiated inresponse to such detection may include initiation of electrical reversalwith associated swapping of concentrate and dilute flows, initiation ofa chemical cleaning (CIP) cycle, or the like. The methods of theinvention may also be used to control boron concentration at any pointwithin a stack or within the system at which control of boronconcentration is desired, based on boron detection in a sample suppliedto the boron analyzer from that point in the system.

For example, the boron reading from a sample collection tube placed at amidpoint of the flow path through an electrodeionization stack may beapplied to control the stack operating potential such that the anionresin along the distal end (e.g., the distal half or two-thirds) of thefluid flow path through the stack remains in a substantially regeneratedstate. This permits optimal electrical efficiency of removal of themajor ionic load of anions, such as chloride, CO₂, SO₄, NO₃ and otherreadily-ionized minerals, in the proximal end of the dilute cells. Italso assures that the distal end is in a highly effective boron removalstate. Other sample points may be employed, alone or as a group. Thus,in a stack or treatment system that has more than one stage, the samplesupplied to the boron analyzer may be taken from a point between stages,while in treatment systems having an ultraviolet (UV) light sourcebetween stages, the sample supplied to the boron analyzer may be from apoint upstream or downstream of such UV light source. When the systemincludes a stack that has electrodes segmented along the length of theliquid flow path, the signal from the analyzer may be applied by thecontroller to regulate the applied voltage, or the current flowingthrough different portions of the stack, so as to optimize overalldemineralization of the feed flow consistent with a given boronthreshold, or may be applied to maximize the removal of boron byassuring that a suitable portion of the flow path remains in a stateeffective to remove boron down to the target level.

In systems with multiple sample points, samples may be supplied to avalve system which is configurable to supply the sample from anyparticular sample outlet to the boron analyzer. Correspondingly, thecontrol system may be programmed to respond to the given detection,optionally in conjunction with a conductivity or other measurement, byregulating the electrical current or voltage of the respective stack orstage from which the sample was supplied, or a related upstream ordownstream unit. The valve system and the control system may be manualor automatic. The valve system may consist of multiple valves, a singlemultiport valve, or a number of multiport valves.

In reversing stacks, that is where the electrical polarity is reversedand the diluting stream compartment becomes the concentrating streamcompartment, the control system may regulate the current or voltagesupplied, or may initiate a reversal sequence or initiate a chemicalcleaning cycle based on the output from the boron analyzer over time.

The sample may be supplied to the boron analyzer from a point along thelength of a product manifold within a stack. By varying the position ofthe sample point along the length of the product (dilute out) manifoldthe performance of any cell in the stack can be determined. After theposition of the point along the length of a product manifold that hasthe highest boron concentration has been determined, that point maycontinue to be used as a control point, providing a sample supply to theboron analyzer during continued operation of the stack.

Embodiments of the invention may include treatment systems with one ormore reverse osmosis units, and vary a condition of RO operation inresponse to a boron measurement. In a UPW treatment system of theinvention having one or more RO units, the outlet fluid may be sampledto a boron detector, and the control system may then apply the boronmeasurement to regulate RO operation so as to optimize the removal ofboron. This is accomplished by one or more steps of setting the highpressure side flow rate to the RO unit, setting or adjusting the brineblowdown rate, and/or by setting the feed rate of one or more chemicalsin the RO system. The control system can, for example, increase highpressure side flow rate, brine blowdown rate, increase product waterpermeation rate, and/or feed rate of chemicals when the boronconcentration is greater than a desired value. It can also or it candecrease high pressure side flow rate, brine blowdown rate, decreaseproduct water permeation rate, and/or feed rate of chemicals in theevent boron concentration is less than the preset value and processingconditions may be relaxed or use of chemicals decreased while stillmaintaining effective levels of removal in the RO or a downstreamportion of the system. In this way, an RO stage or system can beoperated to treat liquids to a predetermined boron concentration withoutthe attention of a human operator and without wasting chemicals suppliedto such stage or system. This method and apparatus may also be used tocontrol the boron concentration at any RO stage or point in thetreatment system by supplying the sample stream to the boron analyzerfrom the point in the system at which control of the boron concentrationis desired and effecting appropriate adjustments in that or anotherstage. In a stage or system having more than one pass, the samplesupplied to the boron analyzer may be from a point between passes. In astage or system having an ultraviolet (UV) light source between passes,the sample supplied to the boron analyzer may be from a point upstreamor downstream of the UV light source. Multiple sample outlets maycommunicate with a valve system operative to supply the sample from anyparticular sample outlet to the boron analyzer such that the controlsystem can regulate more than one, or different ones of, the foregoingstates or conditions in response to boron values at different placesalong the treatment line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a simplified process flow diagram of a treatment system ofthe present invention having an EDI stage or unit;

FIG. 1B is a simplified process flow diagram of a treatment system ofthe present invention having an RO stage;

FIG. 2 is a simplified process flow diagram of another RO embodiment ofthe present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides UPW treatment methods and apparatus withcontrol of filled cell EDI stacks (FIG. 1A) and/or RO units (FIGS. 1B,2) based on or in response to a boron detection or measurement. Theconstruction and operation of a low level boron detector suitable forreal-time, rapid, inexpensive on-line measurement of boron in ultrapurewater used for example to manufacture semiconductor electronic circuitryis described in International Patent Application PCT/US01/24637. Thisinstrument is a convenient (and less costly) measurement instrument thanthe conventional ICP-MS instrument used for low-level boron measurement,and it may be attached on-line to monitor boron levels and confirm waterquality of a boron at the low ppt level to confirm boron free operationof a water treatment system. Other instrumentation can be used to samplehigher levels of boron, or sample boron in the presence of other ions,and may be used to detect boron concentration at earlier stages of atreatment line. This invention applies such measurements to control oneor more membrane-type boron removal units in a process line, where theterm “membrane-type unit” is intended to refer to a unit such as an EDIwater treatment unit that relies on semipermeable membranes exchangemedia with electrical operation, or to a filtration type unit such as anRO unit that relies on selectively permeable membranes without requiringan electrical field or current. The controller may control a conditionof water supplied to electrodeioization or reverse osmosis unit toassure that boron is removed to below a predetermined concentration,which, in various embodiments is a level in part per billion, or subppb, and in fab plants results in a product water that is boron-free,typically in the low parts per trillion. Desirable operating states andinternal flow conditions of a filled cell electrodialysis stack and/orsystem are described in International Patent Application PCI/US01/25226,filed Aug. 10, 2001 and commonly owned with the present invention. Suchbackground knowledge of the typical details of stack operation and theremoval rates and types of ions removed at different regions along theflow path through an EDI stack will be assumed herein. Each of theforegoing international patent applications is hereby incorporatedherein by reference in its entirety.

In one aspect, the present invention includes a system wherein a boronmeasurement is applied to a control system that regulates the electricaldrive of an EDI stack to maintain effective boron removal conditionswithin the stack. In another aspect, a control system may regulateoperating conditions of an RO system to maintain the desired boron setpoint. Systems of the invention may set operating conditions of an RO orEDI unit to achieve one threshold in a first stage, and adjustconditions of a later stage to meet another, lower, level based on boronmeasurements. Systems may also be vary the interface with an existingtreatment plant, effecting a control operation such as varying the blendof feed from a high pH silica removal treatment stage to mostefficiently meet the desired RO feed state condition.

In general, the attainment of a very low boron level may require thatthe starting water to the final boron removal units itself have alimited boron load that is attained by earlier treatment stages startingwith a feed or source water of higher and potentially variable boroncontent greatly above this limit. For example, a groundwater or seawaterraw feed may have 0.2-5 ppm boron, while a feed to a final boron removalstage may have a concentration of 0.5-5 ppb boron. In each case, thefeed may be treated by suitable early stage processes, such as ionexchange beds, boron-specific chelating beds, multiple pass ROtreatment, or other treatment to bring boron level of the source down toa first predetermined threshold or suitable range. In embodimentsdiscussed below, it will therefore be assumed that the starting waterhas a limited boron level, although it may include other minerals athigher concentrations. The invention then applies a boron measurement tocontrol an electrodeionization stack and/or reverse osmosis unit toproduce or maintain defined preselected boron limit, or varies the blendof permeates from different RO units to meet a predetermined level ofboron, in the product water. Embodiments of the invention may befollowed by further treatment, such as a final polish loop in a fabplant. In that case, the resin bottles of the final polish will have agreatly extended life before breakthrough.

In one embodiment of the invention shown in FIG. 1A, a sample stream ofthe product from one or more filled cell electrodialysis stack(s) isdirected, e.g., by a conduit, to the inlet of an on-line boron analyzer.The electronic output of the boron analyzer is sent to a control systemthat adjusts the electrical current or voltage supplied to the filledcell electrodialysis stack(s) and/or system(s). Other possible controlsteps or adjustments includes setting a temperature of water supplied tothe EDI unit to enhance boron removal.

Within the stack, the fluid being treated flows through dilute cellscontaining ion exchange resin, typically in bead form, and the beadscapture various ionic species that then migrate, under the influence ofan applied electric potential, through ion-permeable membranes out ofthe treatment stream. The invention may assume a model wherein, in asingle stage EDI, calcium, chloride and other easily removed ions arepreferentially removed at the front or proximal portion of the fluidpath along the length of the EDI dilutes cells, and the stack is run ata current level such that the exchange resin filling toward the distalend of the fluid path remains in a substantially regenerated state.Boron, although not ionized at neutral pH, is effectively captured if itcontacts regenerated resin in the OH form. Once captured by the exchangeresin, the boron migrates into an adjacent concentrate channel and isflushed, so the EDI unit can effectively remove 95% or more of the boronfrom the feed provided a sufficient length of the distal flow pathremains regenerated. Thus, to optimize boron removal by EDI, thecontroller may respond to detection of increased or increasing boron inthe EDI product water by increasing the drive current to the stack,causing the upstream species (chloride and the like) to be entirelyremoved earlier along the proximal flow path. This assures that thedistal end of the flow path will be in a substantially regenerated form,and will more effectively capture and remove boron from the flow.Similarly, if the boron level falls below a desired set point, or willremain below the desired set point, the controller may operate bydecreasing the EDI drive current, allowing the major front-end ionicburden to be removed at lower electrical flux. When boron removal stillremains effective, operation at lower flux may be desirable to savepower. The controller may, in the alternative apply the detector outputto adjust or control another element, such as chemical injectionupstream of the EDI unit to adjust feed pH, changing the pH to enhancefront-end ion removal, distal end resin regeneration state, or boronionization. One advantageous pH control method is applied to an EDIstack having primarily or only anion exchange resin in an initial frontend portion of its dilute cells; cations producing elevated pH thenremain in the flow to enhance boron removal.

In another embodiment a sample stream of the feed of a filled cellelectrodialysis stack(s) is conditioned by flowing through one or moreion exchange columns capable of removing ions more highly charged thanboron, but not boron itself, and is then provided to an on-line boronanalyzer. Alternatively, suitable conditioning may be performed using ananofiltration or reverse osmosis membrane to reject strongly chargedions while having an insignificant rejection of boron. The output of theboron analyzer is used as an input to a control system that adjusts theelectrical current or voltage supplied to the filled cellelectrodialysis stack(s) and/or system(s), or controls a chemicaladdition or other condition as described.

Systems of the invention may include several stacks in hydraulic series.In this case, preferably a sample stream is taken from a sample tap inthe liquid conduit between the stacks and directed to the boronanalyzer. The boron analyzer output is provided as an input to a controlsystem that adjusts the electrical current or voltage supplied to one orboth series-connected stack(s). The first stack may, for example, becontrolled to effectively remove the major ionic burden, while thesecond stage may be operated in a substantially regenerated mode toassure the highest boron removal. Separate or different-conductivityconcentrate streams may be provided to each stack to optimize theiroperation, and other modifications of the stacks such as layered,monotype or other resin fillings may be used as appropriate for theirrespective feed characteristics and desired steady state operatingconditions. A system may employ a first stack built with only anionresin to allow maintenance of elevated pH of the stream for effectiveboron removal, and the second stack may have a mixed resin filling toremove other ions.

When an electrodeionization stack has its electrodes segmented alongtheir length parallel to the liquid flow path through the cells of thestack, the boron reading of the product stream may be applied toseparately control the current of each electrode segment, so as tooptimize removal of boron in the stack as a whole. The segmentedelectrodes allow one to separately control the rates at which the ionspassing in different regions are removed, without introducing excessivepolarization or water splitting in other regions that might cause theresin to throw salt or otherwise degrade the product stream.

In systems with two or more stacks in hydraulic series having anultraviolet (UV) light source between the stacks, a sample stream may bedirected to the boron analyzer from a sample tap in the liquid conduitdownstream of the UV light source. The output of the boron analyzer isused as an input to a control system that adjusts the electrical currentor voltage supplied to one or more of the stacks.

In systems with multiple stacks and/or stages of ED, EDI and/or ROunits, a preferred embodiment has multiple sample outlets connected toinlets of a valve system with a single outlet that delivers a samplestream to the inlet of an on-line boron analyzer. Valve control signalsor related synchronization signals allow the states and boron levels ofeach sampled stage to be identified, and the output of the boronanalyzer may thus be applied by the control system to control differentones of the units as appropriate to achieve a boron free product. Forexample, the controller may regulate electrical current or voltagesupplied respectively to appropriate ones of the stacks and/or stagesfrom which the sample was supplied, to adjust RO parameters at anupstream stage, or to select from among possible changes based onsecondary (non-boron) considerations, such as cleaning treatment orchemical addition costs, trade-offs in passage of other ions or thelike. The valve system may include multiple valves, a single multiportvalve, or multiple multiport valves, and the valve system and relatedcontrol system may be manual or automatic in operation. If manual,preferably the control system includes a display in which system statescontrol interventions are displayed for the operator.

When the treatment system is one configured for filled cellelectrodialysis reversal (EDIR) operation, that is, when electricalpolarity of an EDI unit is reversed and the diluting stream compartmentbecomes the concentrating stream compartment, then preferably the samplepoint for boron detection is placed in the product outlet line. In thiscase, the controller may apply the analyzer output to initiate areversal sequence, or may determine suitable reversal intervals forperiodic reversal based on the output from the boron analyzer over time.One particularly advantageous mode of operation is to employ amulti-stage EDI treatment, with reversal of only the first stage.

In another aspects of operation, the sample stream may be taken with amovable probe having an inlet movable to different positions along thelength of a product manifold of an EDI stack. By varying the point atwhich said liquid conduit inlet is placed along the length of theproduct manifold, the performance of any diluting cell in the stack canbe determined. After the position of the point along the length of aproduct manifold that has the highest boron concentration has beendetermined, that point may continue to be used as the sample supply tothe boron analyzer during continued operation of the stack.

Systems of the invention may also sample and control treatment plantsemploying one or more reverse osmosis units for production of watermeeting a preselected boron level (MCL), as shown in FIG. 1B. In thiscase, the control system is configured to change one or more operatingconditions of the RO unit. For example, it may control a pump motor,back-pressure or outlet valve, chemical injector or other element, andmay receive inputs from appropriate pressure sensor, conductivity, pH,chemical addition or other sensors, such that the controller regulateshigh pressure side flow rate, brine blowdown rate, and/or feed rate ofchemicals in one or more RO stages or units of the treatment system inresponse to the level of boron measurement. The preferred type of boronanalyzer for boron free product sensing is that described in theaforesaid international PCT patent application PCI/US01/24637,incorporated in this application in its entirety. Such instrument iscommercially available from Sievers Instruments, Inc. of Boulder Colo.,as the UPW Boron Analyzer, an on-line boron analyzer designed forcontinuous measurement of ultra-trace boron contamination, whichprovides continuous, unattended measurement of boron in ultrapure waterdown to 20 parts per trillion. Other measurement devices may be used fordetection of less stringent upstream boron measurement levels.

As relevant to the task of boron removal, operation of a reverse osmosisunit with increased high pressure side flow rate decreases the thicknessof the fluid/membrane polarization or boundary layer, and reduces theconcentration of boron next to the layer of the RO membrane effectingthe separation. Increasing the brine blowdown from the high pressureside of the process decreases the total boron concentration on the highpressure side of the membrane, while increasing the product waterpermeation rate produces a product water with a lower boronconcentration. Chemicals such as polyols (i.e. sorbitol), polymericentities with polyols or other boron sequestering active sites, orcaustic may be added at controlled rates to the RO system feed, or tothe feed of a second or third pass RO system, to increase the rejectionof boron and/or its complexes by the RO membrane. Additives or chemicalagents may be partially recycled by adding an ultrafiltration loop, andblow down may be controlled to maintain effective operation withefficient use of chemicals. The methods and systems embodying methodsaccording to this aspect of the invention perform one or more of thesecontrol interventions in response to the detected boron level.

In one preferred embodiment a sample stream of the product from ROstages and/or system(s) is directed to the inlet of a low level boronanalyzer, e.g., an on-line boron analyzer, which communicates with acontrol system that adjusts one or more of the high pressure side flowrate, brine blowdown rate, and/or feed rate of chemicals in one or moreRO units of a treatment system.

In another embodiment, a sample stream of the feed to RO stages and/orsystem(s) is passed through one or more ion exchange columns capable ofremoving ions more highly charged than boron, but not boron itself, andthis conditioned stream is passed to the boron analyzer. Alternatively,sample conditioning of the feed may be performed by using ananofiltration or a reverse osmosis membrane to reject (remove) stronglycharged ions while having a well-characterized but incomplete rejectionof boron. Such sample preparation may be done for only certain samplingpoints and not others, as appropriate for the particular feed and thevarious treatment units upstream of each sampling point. Preferably,such conditioning is effected when interfering chemical species occur athigh concentrations in the sample feed to the boron analyzer. Othersuitable conditioning treatments may include specific adsorption orabsorption, addition of specific complexing or sequestering agents,simple dilution, and/or application of standard dilution and/or standardaddition (such as done before RO to characterize operation).

In systems with two or more RO units and/or stages in hydraulic series,a sample stream from a sample position in the liquid conduit betweenstages is preferably directed to the boron analyzer, and the detectionoutput is applied by a control system as described above to adjust highpressure side flow rate, brine blowdown rate, and/or feed rates ofchemicals (or blow down rate of recycled chemicals) in one or more ROunits or stages of the system. When a UV process is applied between twoRO stages and/or two passes in hydraulic series, a sample stream may betaken from a sample tap in the liquid conduit downstream of the UV lightsource, and its boron level used to control one or more operatingparameters of RO units in the system. It should be noted that when usinga polyol-based boron capture resin or chemistry, a UV unit at adisinfecting wavelength or band, such as a 254 nm UV, is preferably usedto control biogrowth. When the system has multiple passes and/or stages,a preferred embodiment provides multiple sample outlets to a valvesystem having a single outlet communicating directly with the inlet ofan on-line boron analyzer, or having a single outlet communicating withthe inlet of an on-line boron analyzer and one or more outlets thatprovide fluid samples to sample conditioning processes as describedabove connecting with the analyzer.

As for the EDI system embodiments, the valve system may include multiplevalves, a single multiport valve, or multiple multiport valves, and thevalve system and/or the control system may be manual or automatic. Asample stream may also be supplied to the inlet of a boron analyzer frominlets, or a probe having a movable inlet positionable along the lengthof a product manifold of several RO modules. By varying the point atwhich the sample inlet is placed along the length of the RO productmanifold the performance of any module in an RO stage or system is thendetermined. After the position of the point along the length of aproduct manifold that has the highest boron concentration has beendetermined, that point may continue to be used as the sample supplypoint for the boron analyzer during continued operation. For example, ROmodules may be contained in a number of pressure vessels having theirproduct outlets connected to a common manifold for any particular stage.One end of a small diameter tube or pipe may be inserted in the manifoldby a means that allows controlled positioning of the inlet of the tubeor pipe at a point that corresponds to the position in said manifold ofthe product outlet of any of the module(s) of the RO pressure vessel,and the outlet of the tube pr pipe is connected to the boron analyzer.Similarly, the probe may be positioned in the manifold of an array ofvessels, to sample the outputs of the individual vessels, each of whichtypically houses a string of four to eight modules. In this manner arepresentative sample stream, or a “worst case” sample stream, or thestream from any particular branch of the manifold can be directed to theboron analyzer, directly or by way of a preconditioning process.

In one embodiment of a system, a source of water to be treated is passedthrough a gross filter to strain the water and remove largerparticulates, a microfiltration or ultrafiltration membrane or unit, asoftener to remove hardness, and optionally a degassing unit, and the pHof the feed is increased (for example, by adding caustic or otheralkaline liquid, or by other suitable technique), and passed to the highpressure side of a reverse osmosis system. A sample stream from thepermeate side of the RO membrane is supplied to an on-line boronanalyzer which provides a signal corresponding to the concentration ofboron in the sample stream to a control system which regulates the meansused to increase the pH of the feed to the RO (for example by regulatingthe rate at which caustic or other alkaline liquid is supplied to thefeed), increasing the feed (or polyol capture material) if needed tomaintain concentration of boron below a predetermined low level. Forexample, for UPW fab water, the control system may maintain boron below50 ppt, advantageously below 20 ppt and preferably below about 10 ppt.Similarly, for potable water, the system may maintain a 50 ppb level, 30ppb or such level as may be specified. For operation of a fab plant UPWsystem, the system may control an RO stage to produce a low- or sub ppbboron level output, followed by an EDI stage or loop operated to producelow ppt or boron-free product water. The EDI loop may include UV, ionexchange polishers or other treatment of a conventional type. Evenwithout special resins in the EDI unit, removal rates above 95% arereadily maintained, resulting in a removal efficacy such that, iffollowed by a conventional final polish, a greatly extended bottle lifeof 5-10 years is expected.

In an embodiment as illustrated in FIG. 2, a sample stream is suppliedfrom the product outlet of a two-pass RO system with interstage causticinjection. The on-line boron analyzer provides a signal corresponding tothe concentration of boron in the sample stream to a control system thatregulates the rate of caustic supplied to the feed to the second ROpass, and the caustic feed rate is increased as the boron concentrationrises above a predetermined value, and may be decreased as the boronconcentration falls below a lower predetermined value. Rather thaninjecting caustic, the RO feed may come from a previous stage or beintegrated into a system, where a high pH has already been achieved. Inthis case the controller may set a blend rate, or inject a lesser amountof caustic, to obtain the desired decrease or increase of pH. Ratherthan controlling pH, the RO stage removal may be effected using anagent, such as a boron absorbing polyol, a capture agent immobilized insuitably compatible porous polymer phase, microbeads or other systeminjected into the feed. Its rate of injection, or removal, or effectiveresidence time may be set or controlled based on detected boron level.In this case, the agent captures boron while in the stream, is rejectedby the RO; the RO reject may be further passed to a UF unit to separatethe injected capture agent and recirculate it to the RO feed, enhancingresidence time and overall boron removal.

One treatment system having the described low boron controlled outputmay advantageously be implemented by arranging that an existingtreatment plant feed its product or intermediate stage product water toone or more EDI and/or RO units arranged and controlled as describedabove. For example, the treatment systems of the present invention mayreceive water from a final or intermediate stage of treatment line asdescribed in U.S. Pat. No. 5,925,255 or published international patentapplication PCT/US97/14239 (the so-called “HERO” process). In suchcases, the controlled units may receive a feed that has already beencontrolled to a high or low pH, and the system may be configured tooperate for effective boron removal with little or no additionalchemical costs.

It will be apparent to those skilled in the art that changes, additionsand subtractions may be made in the above-described apparatus andmethods for detection and treatment with boron removal, withoutdeparting from the scope of the invention herein, and it is intendedthat all matter contained in the above description shall be interpretedin an illustrative and not a limiting sense. Various modifications ofand variations on the method and apparatus as herein described will beapparent to those skilled in the art, and all such modifications andvariations are considered within the scope of the invention, as limitedonly by the claims appended hereto and equivalents thereof.

1. Apparatus for treating water or other solvent to produce a producthaving a predetermined maximum level of boron, such apparatuscomprising: (a) a treatment line including plural treatment units; (b)wherein the treatment line includes at least one membrane-type boronremoval unit connected for receiving a feed stream of said water orother solvent and providing a treated product stream, the membrane-typeboron removal unit being a unit selected from among the set of unitsincluding a filled cell electrodialysis (EDI) unit and a membranefiltration unit; (c) a sampling outlet providing a sample of said wateror other solvent treated by the treatment line; (d) a boron analyzer;(e) said boron analyzer arranged to provide an output indication ofconcentration of boron in the sample; and (f) a controller, thecontroller applying said indication of boron to set an operatingcondition of the membrane-type boron removal unit such that productwater of the treatment line meets a predetermined maximum level ofboron; further wherein the membrane-type boron removal unit includes anEDI unit and the controller sets an electrical drive condition of theEDI unit.
 2. A method for controlling removal of boron from water orother solvent to produce a portion having a predetermined maximumconcentration of boron in a range of about 500 parts per billion down toabout 10 parts per trillion or less, such method comprising the stepsof: (a) providing a treatment line that includes plural treatment units,wherein the treatment line includes at least one membrane-type boronremoval unit connected for receiving a feed stream of said water orother solvent and providing a treated product stream, the membrane-typeboron removal unit being a unit selected from among the set of unitsincluding a filled cell electrodialysis (EDI) unit and a membranefiltration unit; (b) obtaining a sample of said water or other solventfrom a point along said treatment line by means of one or more samplingoutlets of said treatment line; (c) providing said sample to a boronanalyzer capable of determining on-line and monitoring in real time theconcentration of boron in said sample when the boron level is in a rangefrom above about 500 parts per billion down to at least about 10 partsper trillion or less, wherein said boron analyzer is arranged to providea real-time output indication of concentration of boron in the sample;and, (d) setting a system parameter or an operating condition of themembrane-type boron removal unit in response to the real-time monitoringof the concentration of boron in said sample such that the methodproduces a portion that meets said predetermined maximum level of boronaccording to the following steps: (1) when the membrane-type boronremoval unit is an EDI system, a controller responsive to boronindication adjusts current or voltage supplied, or changes a feedcondition such as pH of the feed stream, or changes other operatingparameters, to achieve said predetermined maximum level of boron; and,(2) when the membrane-type boron removal unit is a reverse osmosis (RO)system, a controller responsive to boron indication controls one or moreof the steps of controlling the high pressure side flow rate, or settingor adjusting the brine blowdown rate, the product water permeation rate,pH, or feed rate of one or more chemicals in the RO system, or changes afeed condition, to achieve said predetermined maximum concentration ofboron.
 3. A method of producing a substantially boron free UPW productwater suitable for semiconductor fabrication, wherein the methodincludes the steps of providing a treatment line including at least onemembrane-type water treatment unit selected from among anelectrodeionization (EDI) unit and a reverse osmosis (RO) unit,detecting a low level boron concentration on line from one or moresampling points along the treatment line, and dynamically controlling anoperating condition of the membrane-type water treatment unit inresponse to said detecting so as to produce said substantially boronfree product water; wherein the step of controlling operating conditionincludes adjusting potential or current across an EDI stack tosubstantially remove ions of a type other than boron so as tosubstantially suppress displacement of boron by said ions of a typeother than boron during treatment.
 4. System for treating water or othersolvent to produce a portion having a predetermined maximumconcentration of boron in a range of about 500 parts per billion down toabout 10 parts per trillion or less, such system comprising: (a) atreatment line including plural treatment units, wherein the treatmentline includes at least one membrane-type boron removal unit connectedfor receiving a feed stream of said water or other solvent and providinga treated product stream, the membrane-type boron removal unit being aunit selected from among the set of units including a filled cellelectrodialysis (EDI) unit and a membrane filtration unit; (b) at leasta sampling outlet providing a sample of said water or other solvent froma point along said treatment line; (c) a boron analyzer capable ofdetermining on-line and monitoring in real time the concentration ofboron in said sample when the boron concentration is in a range fromabove about 500 parts per billion down to at least about 10 parts pertrillion or less, wherein said boron analyzer is arranged to provide areal-time output indication of concentration of boron in the sample;and, (d) a controller in communication with one or more system controlunits, the controller applying said indication of boron to set a systemparameter or an operating condition of the membrane-type boron removalunit such that the system produces a portion that meets saidpredetermined maximum concentration of boron; further wherein, when themembrane-type boron removal unit is an EDI system, the controllerresponsive to boron indication is capable of adjusting current orvoltage supplied, or changing a feed condition such as pH of the feedstream, or changing other operating parameters, to achieve saidpredetermined maximum level of boron; and, when the membrane-type boronremoval unit is a reverse osmosis (RO) system, the controller responsiveto boron indication is capable of one or more of the steps ofcontrolling the high pressure side flow rate, or of setting or adjustingthe brine blowdown rate, the product water permeation rate, pH, or feedrate of one or more chemicals in the RO system, or changing a feedcondition, to achieve said predetermined maximum concentration of boron.5. The system of claim 4, wherein the membrane-type boron removal unitincludes an EDI unit and the controller sets a feed condition of saidwater or other solvent provided to the EDI unit.
 6. The system of claim4, wherein the membrane-type boron removal unit includes an RO unit andthe controller sets an operating condition of the unit or a condition offeed provided to the unit effective to achieve the predetermined maximumlevel of boron.
 7. The system of claim 6, further comprising a treatmentstage effecting boron capture ahead of the RO unit, and the controllercontrols said treatment stage to achieve the predetermined maximum boronlevel.
 8. The system of claim 4, comprising a first stage comprising ROand a second stage comprising EDI, and wherein the controller sets anoperating condition of said first and/or said second stages to achieveone or more predetermined maximum boron levels at one of more stages ofthe treatment line.
 9. The system of claim 4, wherein the treatment linereceives a flow of feed from a stage of a treatment system having anon-neutral pH.
 10. The system of claim 9, wherein the controllercontrols a condition selected from among chemical injection and blendratio to achieve the predetermined maximum boron level.
 11. A method ofproducing a substantially boron free ultrapure water product having amaximum level of boron in the range of about 500 parts per billion downto about 10 parts per trillion or less for semiconductor fabrication orthe like, wherein the method includes the steps of: (a) providing atreatment line for treating a feed stream that includes at least onemembrane-type water treatment unit selected from among anelectrodeionization (EDI) unit and a reverse osmosis (RO) unit; (b)detecting in real time a low level boron concentration in the range ofabout 500 parts per billion down to at least about 10 parts per trillionor less on-line from one or more sampling points along the treatmentline; and, (c) setting a system parameter or an operating condition ofthe membrane-type water treatment unit in real time response to saiddetecting of a low level boron concentration so as to produce saidsubstantially boron free ultrapure water product according to thefollowing steps: (1) when the membrane-type boron removal unit is an EDIsystem, a controller responsive to boron indication adjusts current orvoltage supplied, or changes a feed condition such as pH of the feedstream, or changes other operating parameters, to achieve saidpredetermined maximum level of boron; and, (2) when the membrane-typeboron removal unit is a reverse osmosis (RO) system, a controllerresponsive to boron indication controls one or more of the steps ofcontrolling the high pressure side flow rate, or setting or adjustingthe brine blowdown rate, the product water permeation rate, pH, or feedrate of one or more chemicals in the RO system, or changes a feedcondition, to achieve said predetermined maximum level of boron.
 12. Themethod of claim 11, wherein the step of controlling operating conditionincludes adjusting pH to enhance removal of boron or of competing ions.13. The method of claim 11, wherein the step of controlling operatingcondition includes adjusting an operating condition of an RO unit toproduce said substantially boron free product water.
 14. The method ofclaim 13, wherein the step of controlling an operating conditionincludes a step selected from among the group of steps consisting ofcontrolling high pressure side flow rate, controlling brine blowdownrate, controlling feed rate or concentration of chemicals, controllingblend rate of RO feed, and controlling pH in one or more RO units of thetreatment system.
 15. The method of claim 11, wherein the step ofdetecting a low level boron concentration is performed using an on-lineboron detector having low ppt sensitivity.
 16. A method of producing asubstantially boron free UPW product water suitable for semiconductorfabrication, wherein the method includes the steps of: providing atreatment line including at least one membrane-type water treatment unitselected from among an electrodeionization (EDI) unit and a reverseosmosis (RO) unit, detecting a low level boron concentration on linefrom one or more sampling points along the treatment line, anddynamically controlling an operating condition of the membrane-typewater treatment unit in response to said detecting so as to produce saidsubstantially boron free product water; wherein the step of controllingoperating condition includes adjusting potential or current across anEDI stack so as to maintain anion exchange resin in a distal portion ofthe flow path through the EDI stack in a substantially regenerated statefor effective boron removal.
 17. A method of producing a substantiallyboron flee UPW product water suitable for semiconductor fabrication,wherein the method includes the steps of: providing a treatment lineincluding at least one membrane-type water treatment unit selected fromamong an electrodeionization (EDI) unit and a reverse osmosis (RO) unit,detecting a low level boron concentration on line from one or moresampling points along the treatment line, and dynamically controlling anoperating condition of the membrane-type water treatment unit inresponse to said detecting so as to produce said substantially boronfree product water; wherein the step of controlling an operatingcondition includes providing a boron capture agent upstream of the ROunit and recirculating said capture agent in a loop between an RO brineoutlet and inlet.
 18. The method of claim 17, wherein the loop includesa UF unit for concentrating said capture agent.
 19. Apparatus forsubstantially continuously producing a fluid product stream having aboron concentration equal to or less than a predetermined maximumconcentration from a fluid inlet stream having a boron concentrationabove said maximum concentration, said apparatus comprising: (a) a fluidinlet; (b) at least one boron analyzer unit connected on-line in saidapparatus to receive a sample of the fluid, said analyzer being capableof providing a real-time measure of actual boron concentration in saidsample; (c) at least one membrane-type boron removal unit connectedon-line in said apparatus for receiving a stream of the fluid having aboron concentration above said maximum concentration and for providing aproduct stream therefrom having a reduced boron concentration, said unitbeing selected from a set of boron-removal units including filled cellelectrodialysis units, membrane filtration units and their equivalents;and, (d) at least one controller connected on-line in said apparatus andarranged to apply said real-time measure of actual boron concentrationto regulate on a real-time basis at least one operating condition ofsaid apparatus whereby said apparatus substantially continuouslyproduces said fluid product stream having a boron concentration equal toor less than said maximum concentration.
 20. A method for substantiallycontinuously producing a fluid product stream having a boronconcentration equal to or less than a predeterminable maximumconcentration from a fluid inlet stream having a boron concentrationabove said maximum concentration, said method comprising the steps of:(a) passing the fluid inlet stream into a treatment system, saidtreatment system comprising at least one membrane-type boron removalunit connected on-line in said system for receiving the fluid inletstream and for providing a product stream therefrom having a reducedboron concentration, said unit being selected from a set ofboron-removal units including filled cell electrodialysis units,membrane filtration units and their equivalents; (b) passing a sample ofthe fluid to a boron analyzer unit connected on-line in said treatmentsystem, said boron analyzer unit being arranged to provide a real-timemeasure of actual boron concentration in said sample; and, (c) adjustinga treatment system operating parameter on a real-time basis in responseto said real-time measure of actual boron concentration in said sampleso as to substantially continuously recover from said treatment systemsaid fluid product stream having a boron concentration equal to or lessthan said predeterminable maximum concentration.
 21. A method whereby afluid sample is withdrawn from a fluid treatment system and providedon-line to a real-time boron analyzer for monitoring boron concentrationin said sample in order to regulate one or more fluid treatment systemparameters to produce a substantially continuous flow of treated fluidhaving a very low concentration of boron, said method comprising thesteps of: (a) passing a stream of water or other fluid comprising boronto at least one membrane-type boron removal unit connected on-line insaid treatment system; (b) providing a sample of said water or otherfluid on-line and on a real-time basis to said real-time boron analyzer;and, (c) regulating one or more treatment system parameters using acontroller connected on-line in said system and arranged to control oneor more operating conditions in said system in response to boronconcentration readings from said boron analyzer whereby treated water orother fluid from said system maintains a concentration of boron equal toor less than a predetermined maximum boron concentration.
 22. Apparatusfor controlling removal of boron from water or other fluid on areal-time basis comprising: (a) at least one membrane-type moduleconfigured to remove boron from said water or other fluid; (b) a conduitfor providing a portion of water or other fluid from such apparatus; (c)a real-time boron analyzer with inlet for receiving said portion fromsaid conduit, (d) a signal output from said boron analyzer for at leastproducing a signal that corresponds on a real-time basis to the analysisof actual concentration of boron in said portion; and, (e) a controllerresponsive on a real-time basis to signals from said boron analyzer foradjusting operating parameters of said apparatus on a real-time basis tocontrol the removal of boron.
 23. Apparatus for controlling removal ofboron from water or other fluid on a real-time basis, said apparatuscomprising: (a) a source of water or other fluid having a boron content;(b) one or more membrane-type unit operations or equivalents thereofadapted to remove boron from said water or other fluid; (c) a conduitfor providing samples of said water or other fluid from at least onelocation before, within and/or after said one or more membrane-type unitoperations; (d) a real-time boron analyzer in communication with saidconduit for performing real-time analyses of actual boron concentrationin said samples; and (e) output components responsive on a real-timebasis to said analyses and adapted to control and/or regulate operatingparameters of said apparatus to maintain predeterminable values ofactual boron concentration in said at least one location.